1. Field of the Invention
The present invention relates to the fabrication of corrugated board from paper web. Specifically, the present invention relates to the control of wrap guide rollers for web preheating cylinders. Also, a new bonding nip and product pulling section is described having unique value for continuously laminating double faced board from polymer plastic coated paper webs.
2. Description of the Prior Art
In the fabrication of corrugated board from paper webs, it may be desirable to heat one or more of the constituent webs to a predetermined temperature prior to bonding or corrugating.
There are several reasons for web preheating such as that disclosed by K. B. Lord in U.S. Pat. No. 3,004,880 for curl correction and that disclosed by W. P. Sorenson in U.S. Pat. No. 3,694,927 for adhesive cure acceleration. U.S. Pat. No. 3,960,475 to J. Deligt et al describes the use of steam heated cylinders to plasticize a polymer plastic coating on a paper web for fusion bonding a corrugated liner with a corrugated medium web.
Regardless of the objective, when preheating cylinders are used to heat a traveling web, it is desirable, if not necessary, to control the magnitude of web wrap about the cylinder. Since the web path to and from the preheating cylinder is normally fixed, it is conventional to provide a wrap guide roller having an orbital path about the preheating cylinder to adjust the location about the preheating cylinder periphery at which the web first contacts the preheating cylinder surface. Moreover, if more than approximately 200.degree. of preheating cylinder surface is to be made available for effective web heating, it is known to provide two such orbiting wrap guide rollers; the angular location of an outer orbit or secondary wrap control roller having a fixed ratio relationship to an inner orbit or primary wrap control roller.
The K. B. Lord patent, supra, describes a double face corrugated board laminating machine wherein both, the flute tips of prior laminated single face web and the double face liner, are heated by means of preheating cylinders. The Lord patent disclosure also includes an automatic control system for sensing the single face or liner web temperature as the independent control variable immediately prior to entering the double face laminating nip. The angular setting of the Lord wrap control arms respective to each preheating cylinder is determined by a fixed ratio relationship between the actually sensed web temperature and a set-point signal derived from the relative magnitude of finished board curl.
One objective of the present invention is to provide a web preheating cylinder wrap arm control system suitable for bonding 0.008 to 0.010 inch (0.203 mm to 0.254 mm) thick paper web coated with a thin film, 0.001 to 0.00075 inch (0.025 mm to 0.019 mm), of polymer plastic such as polyethylene, polybutylene, buty rubber, polyisobutylene polyvinylbutylene, polymethylmethacrylate, polyvinylchloride, and polyamides. Under this circumstance, no adhesives are used in the laminating process, the respective liner and corrugated medium webs being welded together by thermal fusion of the plastic coatings. The technique requires .+-.5.degree. F. regulation of the 210.degree. F. fusing temperature for the plastic coat lamina. If overheated, the plastic coat develops pinholes to destroy the moisture barrier effectiveness of the coat. If underheated, poorly fused and weak joints between the liner and the corrugated medium results.
When the number of parametric variables affecting lamination of such plastic coated webs are considered, the relatively simple temperature control feedback system disclosed by the Lord patent is found insufficient. Such variables may include (1) the temperature and flow rate of heating steam to the preheating cylinder, (2) the running speed of the laminating machine, (3) the thickness and/or density of the web. An operational example may be found in a production machine which changes frequently between different web weights. The response ratio between an angular set change in the position of a wrap control roller and a control signal error differential will vary respective to the different web weights due to respective heat transfer characteristics. Similarly, any predetermination of response control ratios presumes the existence of certain fixed operating conditions. Should the heating steam temperature and/or flow rate change, the response ratio will be directly affected.
It is, therefore, another object of the present invention to provide an automatic control system for a preheating cylinder wrap arm having a very short feedback signal interim wherein the signal/mechanical response ratio may be quickly and conveniently adjusted by the machine operator.
An additional object of the present invention is to teach the construction of a double facing fusion nip uniquely valuable in forming double faced corrugated board from polymer plastic coated web.